BULLETIN OF CANADIAN PETROLEUM GEOLOGYVOL. 42, NO 3 (SEPTEMBER, 1994), P312-331

Geology and hydrocarbon habitat in a rift setting: southern Gulf of Suez, Egypt

A.S. ALSHARHAN AND M.G. SALAHDesert and Marine Environment Research Centel;

U.A.E. University, P.O. Box: 17777Ai Ain, United Arab Emirates

ABSTRACT

The southern Gulf of Suez in Egypt is located at the junction of the African and Arabian plates, and has excellenthydrocarbon potential. The stratigraphic units in the area are grouped into two main megasequences, the pre-rift (Pre-Oligocene) and the syn-rift (Oligocene-Recent) lithostratigraphic units. Gravity, magnetic, seismic and well data wereused to delineate outlines of several narrowly elongated northwest-trending depositional troughs, separated by struc-tural ridges. Several pre-rift and syn-rift rich source units occur and are mature enough in the deep troughs to generatehydrocarbons. A geochemical study of source rocks and oil samples showed two groups of oil: 1. Gulf of Suez oilsfrom pre-rift sediments; and 2. southern Gulf of Suez oils from Middle Miocene carbonates. The reservoirs are alsoclassified into: 1. pre- rift reservoirs, such as fractured and weathered Precambrian basement, Nubia sandstone,Cretaceous sandstone and fractured Eocene limestone; and 2. syn-rift reservoirs such as Lower and Middle Miocenecarbonates and sandstones. Most oil fields in the region have multiple, producing reservoirs. The Miocene EvaporiteGroup forms the primary seal for most of the reservoirs, and the shales and dense carbonates of both the pre-rift andsyn-rift sections form secondary seals. Trap types include structural, stratigraphic and combination traps. The southernGulf of Suez, which shares more than one-third of the whole Gulf of Suez reserves, remains high in hydrocarbonpotential with many untested plays.

RESUME

La partie sud du golfe de Suez en Egypte est situee ala jonction des plaques africaine et d' Arabie, et possede unexcellent potentiel de decouvertes d'hydrocarbures. Les unites stratigraphiques dans la region sont regroupees en deuxmegasequences principales, I'unite litho stratigraphique du pre-rift (pre-Oligocene) et celIe du syn-rift (Oligocene-Recent). Des donnees gravimetriques, magnetiques, sismiques et de forages furent employees afin de delineer les con-tours de plusieurs fosses de sedimentation etroites et allongees en direction nord-ouest, separees par des cretes struc-turales. Plusieurs unites de roche mere pre-rift et syn-rift sont presentes et sont suffisarnrnent matures dans les fossesprofondes pour produire des hydrocarbures. Une etude geochimique d'echantillons de roche mereetde petrole demon-tra qu'il existe deux groupes de petroles : I) les petroles du golfe de Suez, formes dans les sediments pre-rift et 2) lespetroles de la partie sud du golfe de Suez, qui provinrent des roches carbonatees du Miocene moyen. Les reservoirssont aussi classifies en I) reservoirs pre-rift, telsque les roches fracturees et desagregees du socle precambrien, Ie gresnubien, les gres du Cretace et les calcaires fractures de l'Eocene; et en 2) reservoirs syn-rift leis que les roches carbon-atees et les gres du Miocene inferieur et moyen. La majeure partie des champs petroliferes de la region possedentplusieurs reservoirs productifs. Le groupe des evaporites du Miocene forme la barriere etanche principale pour la plu-part des reservoirs, tandis que les schistes argileux et)es roches carbonatees sans porosite des coupes pre-rift et syn-riftforment des unites de scellement secondaires. Les types de pieges incluent les pieges structuraux, stratigraphiques etcombines. La partie sud du golfe de Suez, qui renferme plus d'un tiers de toutes les reserves du golfe de Suez, demeuretine region a potentiel eleve en hydrocarbures qui recele des zones et qui n'ont pas encore ete testees.

Traduit par Marc Charest.

INTRODUCTION

The Gulf of Suez is a rift zone that runs in a northwest-.southeast direction and forms an elongated depression ofabout 320 kIn in length (Fig. 1). It is bounded by two majorsets of marginal faults. The most characteristic topographicfeatures of the area are the exposures of huge Precambrianbasement blocks at three different localities: Gebel Zeit,

Shadwan Island and Esh El Mellaha Range (Fig. 2). The latterhas a full, pre-rift sequence where it plunges to the south cov-ered by the Miocene reef complex of the Gebel Abu Shaar(Fig. 2).

Oil was first found in the Gulf of Suez in 1886 when crudeoil seeped into tunnels which were dug for extracting sulphurin the Gemsa area on the western coast of the Gulf of Suez.

312

GEOLOGY AND HYDROCARBON IJAB/TAT IN A RIFT SETTING: SOUTHERN GULF OF SUE4 EGYPT 313

Fig. 1. Location map of the Gulf of Suez (A) with regional structural setting of the Gulf of Suez (8) (sources: Moustafa, 1976; Rashed, 1990;and Hammouda, 1992).

were described by Sadek (1959), Kostandi (1959), EGPCStratigraphic Committee (1964), Issawi (1973), Webster(1982), Be1eity (1982), Sellwood and Netherwood (1984),Salah (1989), and Ayad and Stuart (1990) as summarizedbelow.

Since then, the drilling was conducted close to the surface oilseeps in the west coastal strip of the southern Gulf of Suez.This resulted in the discovery of the Gemsa Oil Field in 1907,the first discovery in the Middle East. The exploration contin-ued in the onshore area and in the adjacent islands until theSecond World War. Exploration activity resumed in 1961 andhas continued since. It has resulted in the discovery of suchmajor oil fields as Zeit Bay, Shoab Ali, East Zeit, Geisum andAshrafi (Fig. 2).

The principal aim of this paper is to define the geology, thehydrocarbon potential and the tectonic influence on hydrocar-bon generation, migration and accumulation within the south-ern Gulf of Suez. The term, "southern Gulf of Suez", isapplied in this study to the area that is bordered by longitudes34006' and 330 27' E and latitudes 270 23' and 27057' N (Fig.2).

STRATIGRAPHY

The stratigraphic sequence in the study area ranges fromPrecambrian to Recent and can be classified into two megase-quences: pre-rift and syn-rift (Fig. 3). The stratigraphic timeand rock units, determined by examinations of outcrop sec-tions, subsurface cores, an electric logs as well as microfaunaland palynological studies from ditch samples and thin sections,

PRE-RIFT LITHOSTRATIGRAPHIC UNITS

The pre-rift stratigraphic section ranges from Precambrian

to Late Eocene (Fig. 3).

PRECAMBRIAN BASEMENT

Basement rocks have been penetrated to depths rangingfrom 1000 to 5000 m depending on the drilling site, and areinterpreted as granitic on the basis of petrophysical and struc-tural similarities with their surface exposures. The basement ishighly weathered and intensively fractured in response to thetectonic activity in this area.

PALEOZOIC-EARLY CRETACEOUS CLASTICS

The term Nubia sandstone is applied for the Palaeozoic-Early Mesozoic clastic section which lies unconformably overthe basement. Pollens and spores were used to determine geo-logical ages of the Nubia facies. The Nubia sandstone consistsof four units in ascending order: Nubia D and C (Early

314 A.S. AI..5HARHAN and M.G. SAlAH

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Fig. 2. General geology and well locations of the southern Gulf of Suez (modified from Salah,1992).

,.North Ras.~

Bahar(1-3

315GEOWGY AND HYDROCARBON HABITAT IN A RIFT SETTING: SOUTHERN GULF OF SUEz. EGYPT

Paleozoic), B (Carboniferous), and A (Early Cretaceous).Nubia B is a dark shale with very minor sand streaks while

units A, C and D are predominantly sandstone with thininterbeds of shale. The total Nubia ranges in thickness fromabout 23 to 427 m, and was deposited in a continental to shal-low marine setting.

CENOMANIAN-LOWER SENONIAN SUCCESSIONThis Cretaceous clastic sequence consists of four forma-

tions in ascending order: Raha (Cenomanian), Abu Qada(Cenomanian), Wata (Turonian), and Matulla (lowerSenonian). In the outcrops, these formations are considered asone unit (known as the Cretaceous clastics) which lies uncon-formably over the Nubia sandstone. In the subsurface it is easyto identify the Matulla Formation; however, the three otherformations are difficult to differentiate due to the interfinger-ing of different facies and lack of diagnostic fossils.

The Raha, Abu Qada and Matulla formations consist mainlyof sandstone, shale and carbonate interbeds while the WataFormation consists predominantly of carbonates with thininterbeds of shale. These formations were deposited in amarine, inner sublittoral to littoral setting.

CAMPANIAN-MAASTRICHTIAN SUCCESSIONThese are the youngest Cretaceous sedimentary rocks in the

stratigraphic section. They consist of two formations, theBrown Limestone (early Campanian) and Sudr Chalk (lateCampanian to Maastrichtian). These rocks consist predomi-nantly of limestone with interbeds of highly calcareous shale.The lower part of the succession contains a pale brown chertwhile the upper part is more argillaceous. The two combinedformations range in thickness between about 15 and 106 m inthe northern part of the southern Gulf of Suez, but are absentin most of the wells drilled in the southern part due to erosionand/or non-deposition. The Brown Limestone Formation con-formably overlies the Matulla Formation. These sedimentaryrocks were deposited in a marine, sublittoral setting.

PALAEOCENE SUCCESSIONThe section, known as the Esna Formation, consists of soft,

fossiliferous shale. The Esna Shale never exceeds 21 m inthickness and conformably overlies the Sudr Chalk of theCretaceous Carbonate Group. The Esna Formation wasdeposited in a marine, outer sublittoral to upper bathyal set-

ting.

EOCENE SUCCESSIONThe Thebes Formation consists of the Eocene sediments

and is well represented in the surface section on the back ofthe Esh El Mellaha Range, where it attains a thickness ofabout 122 m. In the subsurface section the unit did not exceeda thickness of more than 61 m. The Thebes consists mainly oflimestone with very thin streaks of shale and conformablyoverlies the Esna Shale. It was deposited in a marine outersublittoral setting.

OLIGOCENE SUCCESSIONThe Abu Zenima Formation is Oligocene in age and is

present in only one well (Zeit Bay-I, see Fig. 2) in the south-ern Gulf of Suez, with a thickness of about 122 m. The forma-tion unconformably overlies the Thebes Formation and con-sists of interbedded limestones, sandstones and shales,commonly with a reddish colour. The formation was depositedin a continental setting.

EARLY MIOCENE SUCCESSIONThis section is known as the Gharandal Group and consists

of two formations from base to top: Nukhul and Rudeis.The Nukhul Formation is the oldest in the Miocene strati-

graphic sequence and unconformably overlies the Eocenelimestone over much of the southern Gulf of Suez. TheNukhul Formation consists of highly calcareous shale withinterbeds of sandstone, carbonate and occasional anhydrite inthe upper part of this section. The formation is well representedin the study area but varies in both facies and thickness, rang-ing between 10 to 730 m. The Nukhul Formation was depositedin fluviatile, open marine to lagoonal setting.

The Rudeis Formation varies greatly in lithology and thick-ness in response to the irregular paleorelief over which sedi-mentation took place. It consists mainly of shale and limestoneinterbedded with sandstone. The unit varies in thickness fromabout 11 to 1304 m. The depositional setting of the RudeisFormation is considered shallow to deep marine.

MIDDLE MIOCENE SUCCESSIONThis succession is known as lower Ras Malaab Group and

consists of two formations from base to top: Kareem andBelayim.

The Kareem Formation conformably overlies the RudeisFormation and consists mainly of interbedded sandstone, shaleand carbonates with thin streaks of anhydrite in the lower partof the section. Generally, the sand per centage increasestoward the marginal boundaries (Tawfik et al., 1992). Thethickness of the Kareem Formation in the southern Gulf ofSuez varies from 15 to 539 m. The depositional setting of theKareem Formation was shallow, partly open marine, withlocalized lagoonal conditions.

The Belayim Formation represents the beginning of themain Miocene evaporitic cycle. It ranges in thickness from 53to 427 m and was deposited in a lagoonal to shallow marinesetting. It is subdivided into four members in ascending order:Baba, Sidri, Feiran and Hammam Faraun.1. Baba Member: This is composed mainly of anhydrite with

subordinate shale. The member ranges in thickness from 14to 81 m in the southern Gulf of Suez.

2. Sidri Member: This consists mainly of shale with thinstreaks of limestone and/or sandstone. It is the thinnestmember of the Belayim Formation with a maximumrecorded thickness of 13 m in the study area.

3. Feiran Member: This is r:nainly composed of halite withanhydrite and thin shale interbeds. The thickness of thismember ranges between 27 and 174 m. Generally, itincreases in thickness southward due to salt withdrawal.

SYN-RIFr LITHOSTRAllGRAPHIC UNITS

The syn-rift stratigraphic section ranges from Oligocene toRecent (Fig. 3).

A.S. ALSHARHAN and M.G. SALAH316

Fig. 3. Stratigraphic column of the southern Gulf of Suez (sources: Barakat, 1982; Khalil and Meshref, 1988; Salah, 1992; and Hammouda,1992).

317GEOLOGY AND HYDROCARBON HABITAT IN A RIFT SETTING: SOUTHERN GULF OF SUEZ, EGYPT

4. Hammam Faraun Member: This consists of shale with sandand/or limestone or dolomite interbeds. The sand ratioincreases toward the basinal margins. The member rangesin thickness from 6 to 152 m.

LATE MIOCENE SUCCESSIONThe late Miocene succession is collectively known as upper

Ras Malaab Group and contains two formations, South Ghariband Zeit.

The South Gharib Formation lies conformably over theBelayim Formation and consists mainly of halite with someanhydrite and shale interbeds. Locally it contains some sandsin the marginal areas. The thickness of this formation variesfrom 46 to 2,286 m. The environment of deposition of theSouth Gharib Formation is considered to have been a restrictedto a shallow marine setting.

The Zeit Formation conformably overlies the South GharibFormation and consists mainly of interbeds of anhydrite andshale with some salt bodies in parts. Sands are recorded espe-cially in the marginal areas. The formation varies in thicknessfrom 26 to 914 m. The Zeit was deposited under alternatingrestricted and open marine conditions to shallow marine set-

ting.

POST MIOCENE SUCCESSIONThe post-Miocene sediments and sedimentary rocks are

known as the post-Zeit Formation of Pliocene to Recent age.The thickness and lithology of these sediments show a markedvariation from one place to another within the southern Gulf ofSuez. Generally, they consist of sand and sandstone, shaleand/or carbonate with thin streaks of anhydrite.

be considered as a failed rift. Generally, the Gulf of Suez issubdivided into three tectonic provinces that are separated bytwo accommodation or hinge zones, Zaafarana in the northand Morgan in the south (Fig. IE). The central tectonicprovince is characterized by NE dip while the northern andsouthern provinces are characterized by SW dip as describedby Meshref (1988) and Khalil (1988).

A cross-section across the southern Gulf of Suez showsdrastic topographical relief with denuded basement reachingelevations of nearly 2000 m on the flanks (Fig. 4). Its deepestdepocenters along the axial trough have over 5000 m ofNeogene syn-rift sedimentary rocks (Evans, 1990).

Both surface and subsurface data were used to establish thegeometry of the southern Gulf of Suez. Aeromagnetic andseismic interpretation, surface outcrop patterns on both sidesof the southern Gulf of Suez and the subsurface data fromsome wells in the area were integrated to define the geometryof the southern Gulf of Suez. A relief map on top of the base-ment was constructed to show the structural configuration ofthe southern Gulf of Suez (Fig. 5). The interpretation of thesedata showed that the southern Gulf of Suez consists of elon-gate troughs separated by high trends (elongated structuralhighs), both trending NW-SE. The stratigraphic successionand depth to basement vary from one structural high to anotherand also vary within the same high. These highs are dissectedby major cross-gulf trending faults named as cross faults(Meshref et at., 1988).

The major troughs in the southern Gulf of Suez are, fromnortheast to southwest: Eastern, Ghara-East Shadwan, EastZeit, West Shadwan, and Gemsa (Fig. 6). On the other hand,the highs (shown also as Trends in Fig. 6) are: Eastern, ShoabAli, B, Islands, Geisum, Hareed, Ras Bahar, Gemsa, Felefel,and Coastal.

HYDROCARBON HABITAT

The hydrocarbon potential of the study area is generallyhigh because: 1. rifting tends to produce both restricted andopen marine settings favorable to a source rock accumulation.Relatively high geothermal gradients would help convertorganic matter in the source rocks to hydrocarbons; 2. subse-quent rotational faulting and marginal uplifting produce clasticsystems from the mature shield terranes and form shoal areaswhere porous reef buildups and dolomitized limestones, poten-tial reservoirs, could develop; and 3. rotational faulting ofthese units produce structural traps, which may be sealed byonlapping basinal mudrocks or evaporites during later thermalsubsidence of the rift.

SOURCE ROCK POTENTIAL

The source rock potential of the southern Gulf of Suez hasbeen studied by many authors, such as Rohrback (1982),Barakat (1982), Shaheen and Shehab (1984), and Salah (1992).

SOURCE ROCK RICHNESS AND TYPEFive potentially rich source rock intervals have been identi-

fied on the basis of total organic carbon content (TOC) and

STRUCTURE

The northern end of the Red Sea rift -a large tensional fea-ture caused by the separation of the Arabian plate from theAfrican plate -forms the Gulf of Suez. It is an elongateddepression running in a NW-SE direction (Said, 1962) (Fig.1). This tectonic basin is approximately 60 to 80 kIn wide andcontains a sedimentary prism about 3-5 km thick, rangingfrom Miocene to Recent (James et al., 1988).

The Suez rift started between 24 and 21 Ma, or the latestOligocene to the earliest Miocene (Evans, 1990). Rifting wascaused by tensional stresses transmitted through the litho-sphere in addition to an upwelling of hot asthenosphere. Inother words, the Gulf of Suez rifting was passive (Hammouda,1992). Both the crustal extension and tectonic subsidence ofthe axial trough reached their peaks between 19 and 15 Ma(Steckler et al., 1988). However, between 20 and 17 Ma, theflanks of this basin began to be lifted up due to heating effect(Steckler, 1985).

By 15 Ma, the movement along the Aqaba-Jordan rift (ortransform fault) had begun (Fig. 1, Bartov et al., 1980). By 5Ma, this transform fault replaced the Gulf of Suez as the pri-mary plate boundary between the African and Arabian plates(Evans, 1990).

The geometry of the fault system in the basin indicates thatthe area is in an extensional setting, and the Gulf of Suez can

318 A.S. ALSHARHAN and M.G. SALAH

~i-SUEZ RIFT SINAI

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Fig. 4. Cross section across the southern Gulf of Suez (modified from Moretti and Chenet, 1987).

troughs in the southern Gulf of Suez. The location of thesemodelled sections is shown in Figure 8D. These sections wereconstructed based on seismic and magnetic measurements.

The geothermal gradient of most of the drilled exploratorywells in the Southern Gulf of Suez was calculated from theavailable drillstem tests, electric logs and temperature surveysafter correcting the bottom hole temperature. These correctedreadings were used for calculpting the time-temperature index(TTI) on the burial history diagrams (Fig. 8B). This type ofmultiparameter approach is considered necessary to adequate-ly assess the maturity of the source rocks in the southern Gulfof Suez. As this part of the Gulf of Suez is characterized bythe heterogeneity of crustal thickness (Salah, 1989), there aresome hot spots which gave rise to localized source kitchenseven within shallow depths (Salah, 1992). The syn-rift sourcekitchens (primarily Miocene) are the East and West Shadwanand Gemsa troughs (Fig. 8D). The pre-rift source kitchens inthe southern Gulf of Suez from east to west are: EasternGhara, East Shadwan, East Zeit, West Shadwan and Gemsatroughs (Fig. 8D). The Gemsa trough is the deepest kitchen inthe southern Gulf of Suez as the basement reaches to morethan 4600 m in places, which site the pre-rift source rocks inthe gas generation window and even deeper as shown in mod-elled section number 2 (Fig. 8B). The other pre-rift sourcekitchens extend to the Precambrian Basement ranging from2900 to 4000 m, which site the pre-rift sources in the oil gen-eration window, e.g., modelled section number 5 (Fig. 8B).The oil generation threshold (OGT) is believed to have beengenerated 10 Ma for the pre-rift sources, and around 4 Ma forthe syn-rift sources (mainly Miocene) in the southern Gulf ofSuez. The depth to the onset of oil generation ranges in thearea from about 2290 to over 3660 m and decreases southwardwithin the study area (Fig. 8C).

pyrolysis result (S2) within the southern Gulf of Suez (see Fig.7 A). These are in ascending order: Upper Cretaceous carbon-ates (Brown Limestone and Sudr Chalk), Eocene Thebes,Lower Miocene Rudeis, Middle Miocene Kareem, and alsoMiddle Miocene Hammam Faraun Member of the BelayimFormation (Fig. 7 A). BotP the Upper Cretaceous carbonates(an average TOC of 2.5%) and Eocene Thebes (an averageTOC of 1.5%) are the pre-rift deposits formed during theTethyan transgression across northeastern Africa. The RudeisFormation (with an average of 2.5% TOC), and both theKareem Formation and the Hammam Faraun Member (with anaverage of 1.5% TOC) are syn-rift deposits (Fig. 7A). In termsof volumes of well-preserved source rocks, the synriftsequence is more important than the pre-rift. To evaluate kero-gen types, a Van Krevelen-type plot was made using the ana-lytical results of samples from 17 wells in the study area and isshown in Figure 7B which shows that the pre-rift source inter-vals are typically oil-prone (type I) and occasionally oil andgas-prone (type II). The syn-rift source rocks are of multipletypes which may be oil-prone, oil and gas prone or gas-prone(types I,ll and III, respectively, of Tissot, 1984).

SOURCE ROCK MATURITYMaturity was estimated on the basis of vitrinite reflectance

(Ro) and thermal alteration index (TAl) measurements. Tosubstitute the maturity estimate in undrilled areas (particularlyin structurally deeper areas), time-temperature index proposedby Waples (1980) was calculated first from a combined use ofa burial history plot and the geothermal gradient data (See Fig.8 A-C); the equivalent vitrinite reflectance value was then esti-mated. The burial history of the analyzed formations wereinvestigated for nine modelled sections scattered in the main

319GEOWGY AND HYDROCARBON HABITAT IN A RIFT SETTING: SOUTHERN GULF OF SUEZ, EGYPT

EJ";*,;If

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Fig. 5. Relief map on top basement of the southern Gulf of Suez (sources: Salah, 1989; Soudy, 1990 and Fichera et al., 1992). See legend inFigure 2.

A.S. ALSHARHAN and M.G. SAlAH320

Synthetic FaultsAntithetic Faults

D Deep troughsRe9ional dip SW

Wells

Islands

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Fig. 6. Major tectonic elements of the southern Gulf of Suez (sources: Meshref et al., 1988; Rashed, 1990; and Saoudy, 1990).

GEOLOGY AND HYDROCARBON HABITAT IN A RIFT SETTING: SOUTHERN GULF OF SUEZ; EGYPT

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Fig. 7 A. Source rock richness and kerogen types in the southern Gulf of Suez.

OIL STUDYMultiple analytical parameters of seven oil samples (A to

G), collected from both Miocene and Pre-Miocene reservoirs,and several extracts, located in the offshore and onshore areasof the southern Gulf of Suez were used to compare the geneticrelation of the oils in the southern Gulf of Suez with the ana-lytical parameters of the oil in the whole Gulf of Suezdescribed by Rohrback (1982). These analyses included liquidchromatograph separation, gas chromatography, GC-massspectroscopy (GC-MS) and stable isotope mass spectroscopy.The Gulf of Suez oils are interpreted to be of the same geneticfamily, suggesting the same or highly similar source rock of amarine origin (Rohrback, 1982). The analyses of the seven oilsamples from the study area showed that six of these samples(A to F) are genetically different from the Gulf of Suez Oilgroup (group 1), and suggested another group of oils (group2). One sample, G, is similar to the Gulf of Suez oils (Group1) (Fig. 9A-C). The characteristics of Group 2 include lowersulphur content, isotopically heavier, relative increase in C29distribution, pristane/phytane ratio greater than 1.0, abundanceof biomarkers (Gammacerane) and a carbon performanceindex greater than 1.0. The characteristics of this group indi-cate that its source is a non-marine sediment, most probably

Fig. 78. Van Krevelen type diagram for the kerogen types of source. . d ." . d .rocks in the southern Gulf of Suez (reference curves: Tissot and Welte, deposited under hypersalme con iuons (z.e., a restrlcte envl.-1984). ronment).

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322 A.S. AUHARHAN and M.G. SAlAH

() 0 5Km~ IHot Spots Well 1.8 F/100m

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Fig. 8A. Geothermal gradient map of the southern Gulf of Suez (sources: Barakat, 1982; Shaheen and Shehab, 1984; and Salah, 1992).

323GEOLOGY AND HYDROCARBON HABITAT IN A RIFT SETTING: SOUTHERN GULF OF SUEZ, EGYPT

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Fig. 88. Burial history curve of modelled sections of the southern Gulf of Suez (sources: Shaheen and Shehab, 1984; and Salah, 1989). Thelocations of these modelled sections are shown in Figure 80.

A.S. AL5HARHAN and M.G. SALAH324

Well GH 404.8.0001

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basement ranges between 1 and 8%; permeability up to 200md. The basement is granitic in composition and is cut bymafic and acidic dykes. The reservoir properties depend uponcrystal disaggregations caused by weathering of the basementcomplex, and on the tectonic brecciation caused by faultingand fracturing.B -Nubia Sandstone

The Nubia in the southern Gulf of Suez, characterized as amature well-sorted sandstone, forms one of the major pre-riftreservoirs. Its net pay thickness ranges between 30 and 304 m,with the known recovery factor between 15 and 60%. TheNubia is absent in most of the wells drilled in the southern partof the study area while its maximum recorded thickness is 463m in the northern part. Generally it thins southward and yieldsa porosity ranging from 13 to 25% and permeability from 70to 400 md. The quality of the reservoir depends on the amountof shale, the diagenetic processes which may have caused sec-ondary silica dissolution and precipitation, and the depth ofburial. The Nubia produces oil in many fields in the area (Fig.10).

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Vitrinite reflectence (R.)

Fig. 8C. Depth-temperature curve for discovery well GH 404-1 in theHilal Field in the southern Gulf of Suez.

The correlation between the extracts of the rich source unitsshowed two extract types: extract 1 which belongs to the pre-rift source, and extract 2 which belongs to the Middle Miocenesyn-rift (Kareem Formation and Hammam Faraun Member ofBelayim Formation; Fig. 90). Moreover, it showed a closerelation between extract 2 and group 2 oils (Fig. 9E). It isbelieved that the six oil samples within the study area are fromeither Kareem Formation and/or Hammam Faraun Member ofBelayim Formation, as indicated from the oil/source correla-tion. It is normal to have a mixture of group 1 and group 2 oilsin the same field and even in the same pool.

RESERVOIR ParnNTIAL

The southern Gulf of Suez is known for its multi-reservoircharacter where each field produces from several reservoirs(Fig. 10). The reservoirs can be classified into pre-rift reser-voirs and syn-rift reservoirs (for more details see Meshref etal., 1988; Khalil and Meshref, 1988; Salah, 1989; and Tawfiket al., 1992).

PRE-RIFf RESERVOIRSA -Fractured and Weathered Basement

The basement is a common reservoir in the southern Gulfof Suez, where it produces oil/gas in eight fields (Fig. 10) andhas tested hydrocarbons in other discoveries. Porosity of the

C -Cretaceous SandstoneThese are the Matulla, Raha and Abu Qada sandstones

which produce oil from five fields in the southern Gulf of Suez(Fig. 10). Porosity ranges between 15 and 20% and permeabil-ity between 100 and 250 md. The quality of reservoir dependson the depth of the sandstone and amount of argillaceous mat-ter and/or calcareous cement.

D -Thebes LimestoneThis formation is a potential reservoir in the Shoab Ali

Field only and consists of fractured marine carbonates. Theaverage porosity is 12% and the thickness of the net pay is 15 m.

SYN-RIFfREsERVOIRSThe syn-rift reservoirs have greater potential in the southern

Gulf of Suez than the pre-rift because they are better pre-served, well distributed and produced from four formations asfollows:A -Nukhul Formation

The Nukhul sandstone is well developed in the southernGulf of Suez but is locally absent particularly in places thatremained structurally high without being submerged until latertime. The formation thins toward the margins of the Gulf ofSuez and reaches its maximum thickness in the central off-shore area. It produces oil from six fields in the southern Gulfof Suez (Fig. 10). The sandstone is conglomeratic in parts andyields porosities ranging between 17 and 25%.

The Nukhul carbonates of reefal origin produce oil fromtwo fields in the area (Fig. 10). The average porosity of thesecarbonates is 16%. The net pay thickness of the Nukhul reser-voirs (carbonates and/or sandstones) in these fields rangesfrom 21 to 61 m.

B -Rudeis FormationThe Rudeis reservoirs are present over most of the study

area. The Rudeis sandstone has produced oil from four fields

325GEOLOGY AND HYDROCARBON HABITAT IN A RIFT SETTING: SOUTHERN GULF OF SUEz. EGYPT

3340

L H -Oil Field 0 GasFieldC1 = 1000 mLow High

Fig. 8D. Major source kitchens and migration pathways in the southern Gulf of Suez (sources Saoudy, 1990; Shaheen, 1984 and Salah,1992).

A.S. ALSHARHAN and M.G. SAlAH326

Fig. 9A. Oil/Oil correlation, Aromatic Isotope versus Pristane/Phyane Ratio in the southern Gulf of Suez.

fields in the region (Fig. 10). It has an average porosity of 22%and a net pay thickness ranging from about 6 to 36 m. Threemajor alluvial fans of sand are recorded in the southern Gulfof Suez: 1. a northern fan, with a 14% average porosity, whosesource is Gebel Zeit; 2. an eastern fan with a 25% averageporosity, whose source is Sinai Massif; and 3. a southern fanwith a 20% average porosity, whose source is the Esh ElMellaha Range.D -Belayim Formation

The Belayim sandstones (Sidri and Hammam Faraun mem-bers in Fig. 10) produce oil in only one field and have testedhydrocarbons in two discoveries. Two alluvial sand fans wererecorded in the study area, one from the east and the otherfrom the west. The Belayim sandstones have an average poros-ity of 16% with thickness ranging from about 8 to 36 m.

The Belayim carbonates are more important in the southernGulf of Suez than the Belayim sandstones. Hydrocarbons weretested in four discoveries and are being produced from one oilfield in the southern Gulf of Suez (Fig. 10). The Belayim car-bonates are reefal buildups on fault controlled highs and haveporosity ranging between 10 and 19%. The average net paythickness of the Belayim carbonates is about 12 m.

SAC

Representative sample lor the Gull 01 Suez Oils

SEALS

The pre-rift Cretaceous carbonate, Esna shale and Thebeslimestone formations can act as vertical seals over theCretaceous sandstones. Within the syn-rift sequence, however,the Miocene evaporites are always considered to be the ulti-mate seal in the Gulf of Suez (Rashed, 1990). This is particu-larly true in the southern Gulf of Suez where they are generallythick either in the down thrown side of major clysmic faults oron the down dip direction of uplifted tilted fault blocks.However, the magnitude of throw on the c1ysrnic fault is criti-cal in the effective sealing mechanism (Meshref et ai., 1988).A small throw will succeed in juxtaposing the evaporite sec-tion on the down thrown side against the Miocene porous sec-tion on the uplifted block. A large throw will bring theMiocene evaporites in juxtaposition with the Pre-Miocenereservoirs on the uplifted block as at the Hilal Field (Saoudy,1990).

The Miocene clastic section, such as the Rudeis andKareem formations, can act as sealing agents especially inareas where some shaly facies have developed. In such a case,porous intervals within the formation will act as reservoirs,whereas the shaly intervals will become vertical and/or hori-zontal seals, depending on the magnitude of the throw of thefault. The Miocene shales also play an important role in thestratigraphic trap, where they laterally face a body of sand-stone as a facies variation.

Fig. 98. Oil/Oil correlation, Galimove Curve in the southern Gulf ofSuez.

HYDROCARBON ENTRAPMENT

Several mechanisms for hydrocarbon entrapment arerecorded in the southern Gulf of Suez. These are structural,stratigraphic and combination traps, as described in detail byMeshref et at. (1988), Salah (1989), Saoudy (1990) andHammouda (1992).

and tested gas from one discovery (Fig. 10). The net paythickness of the reservoir ranges between about 15 and 30 mwith porosity ranging between 15 and 23% and permeabilitybetween 10 and 1000 md.

The Rudeis carbonates are producers in only three fields(Fig. 10) with an average porosity of 16%. These carbonatesare particularly well developed in submerged high areas withinthe lower Miocene basin, such as in the North Bahar area.

C -Kareem FormationThis is the most important reservoir rock of the southern

Gulf of Suez as it produces hydrocarbons from most of the oil

327GEOLOGY AND HYDROCARBON HABITAT IN A RIFT SETTING: SOUTHERN GULF OF SUEZ, EGYPT

Fig. 9C. Oil/Oil correlation, variation in sterane distribution (C27' C2s' and C29) in the southern Gulf of Suez.

However, in the study area alone, there is only one provenstratigraphic trap at the Ras EI Bahar discovery, where theMiocene porous carbonate wedge is sealed vertically and later-ally by a facies change to dense carbonate. Oil sources wereacross faults or updip from the pre-rift sections.

COMBINATION TRAPS

There are two proven cases of combination traps:

A -Fractured Eocene LimestoneThis limestone's source is itself with an updip contribution

from the Upper Cretaceous carbonates and sealed by syn-riftmudstones as in the Shoab Ali oil field.

B -Reefal BuildupThis is on a fault-controlled high, seal by Miocene evapor-

ites whose source was pre-rift source rocks through a longmigration range, as in the RR 89 discovery. These reefs possessvery high porosity (up to 3%), as in the Miocene reef complexat Gebel Abu Shaar.

STRUCTURAL TRAPSThis is the most important trap type in the southern Gulf of

Suez, where most oil accumulations are trapped structurally(Fig. 11). These traps are represented by:

A -Faulted Structural TrapBoth the pre-rift and syn-rift reservoirs produce oil from a

faulted trap sealed vertically by one of the seals and juxtaposea younger seal on the down thrown side of the fault.Hydrocarbons in this trap are from either pre-rift sourcesacross synthetic faults, or the underlying pre-rift or syn-riftsources as in the Hilal and East Zeit fields.

B -Four Way Dip ClosuresThis trap is present as the hanging wall anticlinal Miocene

reservoirs sealed vertically by intraformational mudstones orMiocene evaporites with sources across or up faults from pre-rift locations.

STRAnGRAPHIC TRAPSThe stratigaphic traps have recently become important tar-

gets for hydrocarbon exploration in the Gulf of Suez in general.

GEOLOGY AND HYDROCARBON HABITAT IN A RIFT SETTING: SOUTHERN GULF OF SUEZ, EGYPT 329

M/Z 191 TERPANES

Fig. 9E. Oil/Source correlation, G.C.M.S. in the southern Gulf of Suez.

Ageof

Reservoir

.:

FARAUN CARBON:;1

DRI SANDSTONESIDRI

CARBONATE

ZEIT BAY I E ZEIT I HILAL SIDKI IGEISUM IASHRAFIIGESMESA

!:>-....OJOJ

C

OJ

u

0

~

E KAREEM SAND"~ KAREEM CARBON

RUDEIS SAND

RUDEIS CARBONATE

.NUKHUL SAND

.: NUKHUL CARBONATE

THEBES LIMESTONE

MATULLA SAND

WATA&RAHA SANDS

"~""a:

~~~

Eocene

===1JJJ~~

=JUpperCretaceous

Pre-cam brianl BA SEMENT

6 3 3 6 5 2 410 4 4 4 4Producing Horizons Number

~Oil EJ Gas~Gas&Oi( *" Undeveloped discovery

Fig. 10. Reservoir potential in the southern Gulf of Suez (sources: Khalil and Meshref, 1988; Salah, 1989; and Saoudy, 1990).

A.S. ALSHARHAN and M.G. SALAH330

sw SEA LEVEL NE-.J

x xx xxxx~

xxxxxxxxxxxx

" " "

~"

"" "--~

x :'x x

xx

xx

X :X X

X X X

xxxxxxxxxxxx

x x x xx x x

xxx:'

xxxxxx'xxxx x xx

xxxxx x x x'XXXXXX;

x x x X :

x x

x

x x x x xx x x x x

x x x x x

x :x x

x x x x xxxxxx

xx x

x :;::~

x

x :'x x i

X X X Xx xx xXX ~XX "X,, X X X X X X ;. X

xx xx XXXX xxx, ~ x x ~X; x x x \ x x "VI., xXx X X X X X X X

X X X X XX X X X X

X X XXFIELRE SERVQIRS SEALSOURCES

\ ~Syn-Rift Sourcex1- Shoab Ali

2- Zeit Bay,Hilal~ Pre-Rift Source

~ Miocene Evaporites

I:::'! Miocene Shale 8.~ dense CarbonateG3 Pre-Miocene Shale II.e9dense Carbonate 3- Geisum. Zeit Bay

4- Ghara

5- North R as Bahar -2

6- Ashrafi a.RR89

--" Fault!!::!] Basement rocks

~ Hammam Faraun

0 Kareem

~ Rudeis

D Nukhul

II:;!1IThebes

0 Cretaceous Sandstones

D Nubia SandstoneI!!:!lJF ractured a.

Weathered Basement

Fig. 11. Hydrocarbon trapping model in the southern Gulf of Suez (modified from Salah, 1989).

ACKNOWLEDGMENTS

We would like to thank Drs. C.G.St.C. Kendall and K.Magara and anonymous reviewers of the journal for reviewingthe manuscript and offering constructive suggestions and rec-ommendations which improved our paper. The co-author ofthis paper would like to thank Drs. W. Meshref (vice chairmanof the Egyptian General Petroleum Corporation) and N. Khalil(chairman of the Egyptian Petroleum Explorationists) for theirfruitful discussion and valuable comments on the differentaspects presented in the paper.

REFERENCES

Ayyad, M. and Stuart, C. 1990. Sequence stratigraphy without seismic tech-niques applied in the Gulf of Suez. 10th Petroleum Exploration andProduction Conference, Cairo, p. 139-213.

Barakat, H. 1982. Geochemistry criteria for source rock, Gulf of Suez. 6thPetroleum Exploration and Production Conference, Cairo, p. 224- 252.

Bartov, Y., Steinitz, G., Ayal, M. and Ayal, Y. 1980. Sinistral movement alongthe Gulf of Aqaba -its age and relation to the opening of the Red Sea.Nature, v. 285, p. 220-222.

Beleity, A. 1982. The composite standard and definition of Paleo events in theGulf of Suez. 6th Petroleum Exploration and Production Conference,Cairo, p. 181-199.

EGPC Stratigraphic Committee 1964. Oligocene and Miocene rock stratigra-phy of the Suez region. Published by the Egyptian General PetroleumCooperation, Cairo, p. 142.

Evans, A.L. 1990. Miocene sandstone provenance relations in the Gulf ofSuez. Insights into synrift unroofing and uplift history. AmericanAssociation of Petroleum Geologists, Bulletin, v. 74, p. 1386-1400.

Fichera, R.,Giori, I. and Milad, G. 1992. Southern Gulf of Suez, integration ofseismic, gravity and magnetic data as constraints 26 in the resolution ofdeep structural setting. II th Petroleum Exploration and ProductionConference, Cairo, p. 31-45.

Hammouda, H. 1992. Rift tectonics of the southern Gulf of Suez. 11thPetroleum Exploration and Production Conference, Cairo, p. 18-19.

Helmy, H. 1988. Structural geology of the B- Trend oil fields, southern Gulf ofSuez. 9th Petroleum Exploration and Production Conference, Cairo, p. 46-68.

Issawi, B. 1973. Nubia Sandstone type section. American Association ofPetroleum Geologists, Bulletin, v. 57, p. 741-745.

James, N.P.,Coniglio, M.,Aissaoui, D.M. and Purser,B.H. 1988. Facies andgeologic history of an exposed Miocene rift-margin carbonate platform.Gulf of Suez, Egypt. American Association of Petroleum Geologists,Bulletin, v. 72, p. 555-572.

+ + + + + + "I+ -+ + I-+ +-1

GEOLOGY AND HYDROCARBON HABITAT IN A RIFT SETTING: SOUTHERN GULF OF SUEz, EGYPT 331

Khalil, B. and Meshrif, W.M. 1988. Hydrocarbon occurrences and structuralstyle of the southern Suez Rift Basin, Egypt. 9th Petroleum Explorationand Production Conference, Cairo, p. 86-109.

Kostandi, A.B. 1959. Facies maps for the study of Palaeozoic and Mesozoicsedimentary basins of the Egyptian region. 1st Arab PetroleumConference, Cairo, v. 2 p., 54-62.

Meshref, W.M., Abu Karamat, M.S. and Gindi, M. 1988. Exploration conceptsfor oil in the Gulf of Suez. 9th Petroleum Exploration and ProductionConference, Cairo, p. 1-24.

Moretti, F. and Chenet, P. Y. 1987. The evolution of the Suez rift: a combina-tion of stretching and secondary convection. Tectonophysics, v. 133, p.229-234.

Moustafa, A.G. 1976. Block faulting in the Gulf of Suez. 5th PetroleumExploration and Production Conference, Cairo, p. 14-38.

Rashed, A. 1990. The main fault trends in the Gulf of Suez and their role inoil entrapment, lOth Petroleum Exploration and Production Conference,Cairo, p. 1-24. '..

Rohrback, B.G. 1982. Crude oil geochemistry of the Gulf of Suez. 6thPetroleum Explorlltion and Production Conference, Cairo, p. 212- 224.

Sadak, H. 1959. The Miocene in the Gulf of Suez region, Egypt. Special pub-lication by the Geological Survey of Egypt., Cairo, 118p.

Said, R. 1962. The geology of Egypt. Elsevier,Amsterdam -New York, 377p.Salah, M.G. 1989. Geology and hydrocarbon potential of the southern sector

of the Gulf of Suez, Egypt. Unpublished M.Sc., Cairo University, 140 p.-1992. Geochemical evaluation of the southern Gulf of Suez, Egypt.

11th Petroleum Exploration and Production Conference, Cairo, p. 383-395.

Saoudy, A.M. 1990. Significance of NE cross faults on oil exploration in thesouthern Gulf of Suez area, Egypt. 10th Petroleum Exploration andProduction Conference, Cairo, p. 104-143.

Shahin, A.N. and Shehab, M. 1984. Petroleum Generation, Migration andOccurrence in the Gulf of Suez offshore, South Sinai. 7th PetroleumExploration and Production Conference, Cairo, p. 126-152.

Sellwood, B. and Netherwood, R. 1984. Facies evolution in the Gulf of Suezarea -Sedimentation history as an indicator of rift initiation and develop-ment. Modern Geology, v. 9, p. 43-69.

Steckler, M.S. 1985. Uplift and extension of the Gulf of Suez. Nature, v. 317,p. 135-139.

-' Berthelot, F.,Lyberis, N. and Le Pichon, X. 1988. Subsidence in theGulf of Suez: implications for rifting and plate kinematics.Tectonophysics, v. 153, p. 249-270.

Tewfik, N., Harwood, C. and Deighton, I. 1992. The Miocene, Rudeis andKareem formations of the Gulf of Suez. Aspects of Sedimentology andGeohistory. 11 th Petroleum Exploration and Production Conference,Cairn, p. 84-113.

Tissot, B.P. and Welte, D.H. 1984. Petroleum formation and occurrence (2nded.) Berlin, Springer-Verlag, 699p.

Waples, D.W. 1980. Time and temperature in petroleum formation applicationof Lopatin's method to petroleum exploration. American Association ofPetroleum Geologists, Bulletin, v. 64, p. 916-926.

Webster, D.l. 1982. Post Eocene Stratigraphy of the Suez Rift, Egypt. 6thPetroleum Exploration and Production Conference, Cairo, p. 76- 189.

Manuscript received: August 24, 1993Revised manuscript accepted: January 10, 1994